Stereocontrolled synthesis of D- and L-beta-rhamnopyranosides with 4-O-6-S-alpha-cyanobenzylidene-protected 6-thiorhamnopyranosyl thioglycosides.

The synthesis of both enantiomers of a 4-O-6-S-alpha-cyanobenzylidene-protected 6-thiorhamnopyranosyl thioglycoside is described starting from D-mannnose and L-arabinose derivatives for the D- and L-series, respectively. This donor is effective in the preparation of the corresponding beta-glycosides using the 1-benzenesulfinyl piperidine/trifluoromethanesulfonic anhydride protocol. Following desulfurization and concomitant debenzylation with Raney nickel, the so-formed 6-thio-beta-mannosides are converted in high yield to the beta-rhamnopyranosides.